Search for something which will produce image thumbnails in the results (such as "kitten photos" or "iphone 4 images")

Click on the first (and seemingly normal) thumbnail in the results

Cover any innocent eyes

Now, do we consider this a bug or a feature? [Thanks, Adam and Dmitry!]

Update: It seems that regular searches are no longer resulting in image thumbnails which makes us think that Yahoo has acted very quickly in order to put an end to this fun. We'll inquire about what happened and update you if we find out.